Conventionally, a superconductive (superconducting) wire material configured such that an intermediate layer is formed on a tape-like substrate made of hastelloy by an ion beam assisted deposition (IBAD) method and an oxide superconducting layer is formed and oriented on the intermediate layer has been known (for example, see Patent Document 1). Also, a superconductive wire material configured such that an epitaxially-grown intermediate layer is formed on a bi-axially oriented substrate and an oxide superconducting layer is formed and oriented on the intermediate layer has been known (for example, see Patent Document 2).
Note that a metal substrate used as a superconductive wire material is called a “superconductive wire material substrate”. Also, a superconductive wire material substrate, on which an intermediate layer is formed by the IBAD method, is typically called an “IBAD substrate”.
A surface of the superconductive wire material substrate goes through each process such as a cold rolling process and a high-precision polishing process, and is processed into a finished surface having a surface roughness Ra of a few nm order (for example, see Patent Documents 3 to 9).
The “surface roughness Ra” is an arithmetic average roughness defined by JISB-0601-2001 (based on ISO4287: 1997).